US special forces troops have arrived in several north African countries over recent months amid Pentagon warnings that the region runs the risk of becoming an al-Qaida recruiting ground and a possible back door into Europe.

Three days before the Madrid bombing, where the first arrests included three Moroccans detained on Saturday, the deputy commander of the Stuttgart-based US European command - which covers all of Africa except the Horn - warned that al-Qaida had an interest in north Africa.

"We have to get ahead of it," General Charles Wald told a group of African reporters in Washington.

Units of around 200 from the US army's 10th Special Forces Group are already installed, or are due to arrive, in Mauritania, Mali, Chad and Niger to train their armies in anti-terrorism tactics and to improve coordination with the US military.

Military cooperation with Algeria, Morocco and Tunisia - where many suspected violent Islamists detained in Europe over the past two years come from - is also being boosted.

Senior US generals, including the commander of the US European command, General James Jones, have been touring the region looking for temporary bases and airfields to use in possible future operations in Africa.

During one such trip last month, Gen Wald told Reuters that armed Islamists "are going to look for a place where they can do the same thing they did in Afghanistan, Iraq or other places. They need a haven to train, equip, organise, recruit.

"As you squeeze the balloon and move them, they are migrating toward Africa."

Unconfirmed reports have already emerged from anonymous Pentagon sources of on-the-ground operations involving the US soldiers.

One carried by Voice of America said US troops on the ground in Mali helped track and drive into the arms of the Algerian army a big haul of weapons due to be delivered to a radical Islamist group there.

The report also suggested they had requested a US air strike against a suspected terrorist target in the desert region of northern Mali and that, although this was turned down, the Pentagon did not rule out such air strikes.

A separate report said a US navy P-3 Orion aircraft guided Chad troops during a two-day battle on the border with Niger last week in which 43 suspected members of Algeria's Salafist Group for Preaching and Combat were killed.

States previously shunned by the international community, such as Algeria, are being provided with arms and military training and may become a cornerstone of US military interests in the region. "We are interested in being able to land at bases in Algeria with our aircraft, or train together," Gen Wald said. "We think we have a lot to learn from the Algerians."

Gen Wald even speculated that Colonel Muammar Gadafy's Libya might one day join the new alliance. "Who knows? Libya could be a part of this in the not too distant future now that they've come back into the western world."

Britain is being brought into the north African alliance as part of a joint European operation called the African Clearing House, he said.

Senior military commanders from several African countries, including General Amari of Algeria, will gather in Stuttgart for a meeting with the Americans next week.

The focus on Africa also comes amid a push by some in the US, especially conservative thinktanks, to do more to secure alternatives to oil from the volatile Middle East. West Africa supplies 15% of US oil and the figure is growing.

A need for the US European command to concentrate harder on north and west Africa may explain why the US Sixth Fleet is considering moving its main base from Gaeta, in Italy, to the southern Spanish port of Rota.

A militant group that has been linked to al-Qaida has been recruiting members from mosques in northern Mali, according to security sources quoted by Reuters. The US state department advised against travel to northern Mali in December, warning that the area had become "a safe haven" for the Salafist Group.

· Greek police discovered a bomb outside a bank in Athens yesterday, but destroyed it in a controlled explosion. The device comprised two sticks of dynamite, a clock and a detonator. Greece has called in Nato to beef up security for the Olympic Games in August.